Generally speaking, when we refer to touch screens, we are referring to 'capacitive' screens. These screens rely on a small electrical current generation which gets disrupted when we touch the screen with bare hands and allow the current to dissipate through our body. You can read more about it here.
When an insulator is introduced between the screen and our skin, the electrical current can't scape and the device can not detect touch. Such is what happens when we wear gloves, and to a lesser extent, when we use screen protectors.
Over the years new technology and manufacturing process has allowed glove manufacturers to incorporate 'touch sensibility' or 'touch compatibility' into the gloves they produce. The question is, why do these type of gloves work?
The challenge that needs to be met is to allow the glove to provide a path for the current to flow away from the device. Therefore, the glove has to become a conductor of electricity. There are two main solutions available, and both have pros and cons.
The easiest solution to implement is to provide a direct path between finger and screen using a conductive thread. The conductive thread can be stitched directly to the glove, and as long as the thread is not broken, current can flow away from the screen unto skin. The biggest advantage for manufacturers using this solution, is that is an inexpensive way to achieve touch, but it does have its drawbacks. As the threads get damaged with use, the current path is broken and touch becomes less and less accurate until it ceases to work. Another drawback of this solution is that the glove has added holes created by the needles, which results in less material integrity and reduced durability.
The other technology used to make gloves touch compatible is layering a conductive fabric on top of the glove structure. Conductive fabrics are made using graphite fibers, which are conductors of electricity, to allow allow the current to scape. There are many suppliers of conductive fabrics, each offering several materials and varied levels of conductivity. Glove designers have to account for several variables before deciding how to make their glove touch sensitive, such as the material durability, its conductivity, how much is needed for the application and where to put it.